The Death Penalty Study was a survey conducted online using a panel of 1,600 U.S. residents 18 years old and older. The sample was provided by Qualtrics, a company that sells samples to marketing and academic researchers. The study was conducted during February-April 2020. People in the study were recruited online using several vendors. The sample is best described as a non-probability, double opt-in panel study. Overall, Qualtrics has access to over 40 million people who have agreed to join online research panels. There are 209 million U.S. residents age 18 and older. So the initial panel (the population of study) includes about 19% of all U.S. adults. 

Quotas. To improve the representativeness of the sample, five demographic characteristics were used to match the sample with known characteristics of the population (U.S. residents). These included age, gender, race/ethnicity, religious affiliation, and political party affiliation. These background characteristics of people are know to influence how they feel about the death penalty.

Approximately 16,000 people were initially recruited from the larger set. Depending on the panel source, people participating in the Death Penalty Study were paid between  $2.00 and $2.50 for completing the online questionnaire. Of the 1,633 people who responded to the survey, 33 were rejected because the quotas described above were already filled. The average length of time to complete the online questionnaire was 12.0 minutes; median time to completion was 9.2 minutes.

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